Chemical methods of wastewater
treatment include neutralization, oxidation and reduction.
Oxidizing methods also include electrochemical treatment. They
are used to remove soluble substances in closed water supply
systems. Chemical purification is sometimes carried out as a
preliminary biological treatment or after it as a method of
post-treatment of sewage.
Neutralization can be carried out by: mixing acidic and alkaline
wastewater, adding reagents, filtering acidic waters through
neutralizing materials, absorbing acidic gases with water or
absorbing ammonia by acidic waters. During the neutralization
process, precipitation may form.
To neutralize acidic waters, use: NaOH, KOH, Na2CO3,
NH4OH (ammonia water), CaCO3, MgCO3, dolomite (CaCO3
· MgCO3), cement. The most accessible reagent is
calcium hydroxide (calcareous milk) with a content
of 5 ... 10% of active lime Ca (OH) 2. Sometimes
waste is used for neutralization, for example slags
of metallurgical
industrial wastewater neutralization.
To neutralize alkaline wastewater, various acids or acid gases
are used, for example, exhaust gases containing CO2, SO2, NO2,
N2O3, etc. The use of acid gases allows not only to neutralize
wastewater, but also to purify the harmful gases from harmful
components.
Oxidation of wastewater pollutants
Oxidative purification method for decontamination of wastewater
containing toxic impurities (cyanides, complex copper and zinc
cyanides) or compounds that can not be removed from wastewater,
and also purified by other methods (hydrogen sulphide,
sulphides).
The following oxidizers are used for wastewater treatment:
gaseous and liquefied chlorine, chlorine dioxide, calcium
chloride, calcium and sodium hypochlorites, potassium
permanganate, potassium bichromate, hydrogen peroxide, air
oxygen, peroxosulfuric acids, ozone, pyrolusite, etc.
In the process of oxidation of toxic contaminants contained in
sewage, as a result of chemical reactions, they pass into less
toxic ones, which are removed from the water.
The activity of a substance as an oxidant is determined by the
oxidative potential. The first place among the oxidants is
fluorine, which due to high aggressiveness can not be used in
practice. For other substances, the oxidation potential is: for
ozone - 2.07; For chlorine it is 0.94; For hydrogen peroxide,
0.68; For potassium permanganate - 0.59.
Oxidation with active chlorine. Chlorine and substances
containing active chlorine are the most common oxidants. They
are used for sewage treatment from hydrogen sulphide,
hydrosulfide, methylsulfur compounds, phenols, cyanides, etc.
Data: 13.03.2017.
